The GNOME project provides two things: The GNOME desktop environment, an intuitive and attractive desktop for users, and the GNOME development platform, an extensive framework for building applications that integrate into the rest of the desktop.

Only apps that have a APPNAME.desktop icon can be added. It's been a complaint of mine for some time. I don't know why it doesn't prompt you to enter some of the information needed and create the file itself, but: